This invention relates in general to imaging, and more specifically to the creation of an electrostatic latent image in the imagewise exposed areas of an electrophotographic imaging member, which in preferred embodiments stands up against time, heat and light.
Recently, a process for stabilizing, or setting, migration imaging electrical latent images has been developed. Such stabilizing processes are disclosed in copending applications Ser. Nos. 349,585; 349,506 and 349,505, all three filed on Apr. 9, 1973. Typically, the process of setting said electrical latent images comprises providing a migration imaging member, electrially latently imaging the migration layer and setting the electrical latent image by either storing the migration layer in the dark or applying heat, applying vapor, or applying partial solvents in a predevelopment softening step. After setting of the electrical latent image, the migration layer can be exposed to activating electromagnetic radiation without loss of the latent image. Also long delays of up to years are possible, between formation of the electrical latent image and the development step which allows selective migration of migration material in depth in a softenable material.
The above-mentioned three stabilizing process applications are based mainly upon a recently developed migration imaging system capable of producing high quality images of high density, continuous tone, and high resolution. Such migration imaging systems are disclosed in copending applications Ser. No. 837,780, and Ser. No. 837,591, both filed on June 30, 1969. In a typical embodiment of the migration imaging system, an imaging member comprising a substrate with a migration layer comprising a layer of softenable material and electrically photosensitive migration material is imaged by forming an electrical latent image on the member, for example by electrically charging the member and exposing it to a pattern of activating electromagnetic radiation such as light. When the photosensitive migration material is layered on or in, but spaced apart from, one surface of the softenable material layer (layer configuration), migration material from the migration layer migrates imagewise toward the substrate when the member is developed by decreasing the resistance to migration of migration material in depth in the softenable layer.
One mode of development entails exposing the member to a solvent which dissolves only the softenable layer. The photosensitive migration material (typically particles) which has been exposed to radiation migrates through the softenable layer as it is softened and dissolved, leaving an image of migrated particles corresponding to the radiation pattern of an original on the substrate with the material of the softenable layer substantially washed away. The particle image may then be fixed to the substrate. For many preferred photosensitive migration particles, the image produced by the above process is a negative of a positive original, i.e., particles deposit in image configuration corresponding to the radiation exposed areas. Those portions of the photosensitive material which did not migrate to the substrate are washed away by the solvent with the softenable material layer. However, positive to positive systems are also possible by varying imaging parameters. As disclosed in the referenced applications, by other developing techniques, the softenable material layer may at least partially remain behind on the supporting substrate with or without a relatively unmigrated pattern of migration material complementary to said migrated material.
It is also known that the imaging members in layer configuration similar to those used herein, can be used as photoreceptors in xerography where the electrostatic image is formed in the relatively unexposed areas. This use is disclosed in U.S. Pat. Nos. 3,573,906 and 3,723,110. While there are known methods for developing the relatively exposed areas of xerographic plate, they typically entail the use of special reversal developer or toner, development electrodes, etc. Now it has been found that a similar photoreceptor may give, in the process of the invention hereof, in a charge, expose process an electrostatic latent image in the imagewise exposed areas which may be developed e.g. by direct xerographic techniques.